Bidirectional circularly polarized antenna with defected ground structure for wideband operation

Abstract

The present work proposes a wideband circularly polarized antenna with novel design to cover the operation over most of the X-band of the microwave frequencies. This antenna is planar and printed on very thin and flexible Rogers’ substrate of material RO3003 with thickness 0.13mm. The antenna structure can be viewed as composed of an elliptic open annular strip that works as the main radiator. Two symmetric parasitic elements of elliptic arc-shaped narrow strips are capacitively coupled to the elliptic strip radiator. The feeding line is coplanar waveguide with defected ground structure. The parasitic elements and the defects on the ground structures help to enhance the bandwidth of both impedance matching and circular polarization. The antenna is designed to produce bidirectional radiation patterns with opposite sense of circular polarization. The design stages to arrive at the final design of the proposed antenna are described in detail. The antenna is fabricated for experimental assessment showing high performance regarding the circular polarization, bandwidth, and efficiency. The proposed antenna has total dimensions of 30×40×0.13mm3. Both the simulation and experimental results show that the antenna impedance is matched to 50Ω over the frequency band 7.5-13.0(54%bandwidth) and the axial ratio is lower than 3 dB over the frequency band 8.85-12.35GHz(33 % bandwidth). It is shown that the antenna gain ranges from 4.5 to 5 dBi, the radiation efficiency is greater than 99 % and the total efficiency is greater than 91 % over the entire frequency band of the proposed antenna.